The present invention relates to rotary work devices that each rotate to cut the distal end surface of a spot welding electrode for use in, for example, an automobile production line away or to detach the electrode from the distal end of a shank.
Spot welding has been conventionally used in an automobile production line. In spot welding, a copper electrode fitted to the distal end of a shank of a spot welding gun is pressed against a steel sheet, and the steel sheet is energized, and is thus resistance-heated to perform welding.
Repetitions of a welding operation cause an oxide film to be deposited on the distal end surface of the electrode, and when welding is performed with the oxide film deposited, the quality of a weld is reduced. Thus, the distal end surface of the electrode needs to be cut away regularly to remove the oxide film. Cutting the distal end surface of the electrode away a plurality of times reduces the length of the electrode. Thus, the electrode need be detached from the shank so as to be replaced with a new electrode.
To address the needs, a rotary work device for spot welding is typically used in an automobile production line to cut the distal end surface of an electrode away and detach the electrode from a shank. A rotary work device described in, for example, Japanese Patent No. 3650928 includes an annular first rotator into which a holder capable of holding an electrode is fitted, an annular second rotator into which a cutter capable of cutting the distal end surface of the electrode away is fitted, and a single drive motor having a vertically extending rotation axis. The first rotator has a periphery including a plurality of uniformly spaced teeth. The second rotator also has a periphery including a plurality of uniformly spaced teeth. The first rotator and the drive motor are coupled together through a plurality of meshed gears, and the second rotator and the drive motor are also coupled together through a plurality of meshed gears. If, while the electrode fitted to the distal end of a shank is held by a holder, the drive motor is rotated, the first rotator allows the electrode to rotate about the central axis of the electrode together with the holder and to be detached from the distal end of the shank. If, while the drive motor is rotated, the distal end surface of the electrode fitted to the distal end of the shank is brought into contact with the cutter, the second rotator allows the cutter to rotate about the central axis of the electrode and to cut the distal end surface of the electrode away.
A suitable rotational speed of the cutter for an electrode cutting operation is significantly different from that of the holder for an electrode detachment operation. For this reason, in Japanese Patent No. 3650928, the outside diameters of the first and second rotators are designed to be significantly different from each other, and the drive motor is rotated at a constant speed. This allows the rotational speed of the first rotator to be different from that of the second rotator.